Unprecedented Relay Catalysis of Curved Fe1–N4 Single-Atom Site for Remarkably Efficient 1O2 Generation

The design of catalysts and catalytic processes for high efficiency and selectivity of important singlet oxygen (1O2) active species generation in oxidation reactions is still challenging, especially utilizing abundant and environmental O2 without photoelectric field or extra thermal condition. Herein, a curved Fe1–N4 single-atom site is developed by incorporating isolated Fe single atom into nanodiamond with high-curvature surface. It leads to an unprecedented relay catalysis route, in which the activation of O2 is coupled with peroxymonosulfate (PMS) activation, to efficiently generate 1O2 species. In detail, PMS is first activated on the curved Fe1–N4 site with electron donation to Fe single atom, accompanied by 1/2 equiv of 1O2 production. More importantly, due to the compressive strain of the curved Fe1–N4 site with a higher energy level of Fe 3dz2 orbital, the curved Fe1–N4 site with electron charge acquisition can directly transfer electron to O2 molecule and consequently trigger the generation of additional 1 equiv of 1O2. Taking advantage of this tandem process, remarkable efficiency and near 100% selectivity of 1O2 generation are achieved, which leads to an ultrahigh metal catalytic efficiency of 0.77 min–1 for tetracycline oxidative degradation and an outstanding catalytic performance for benzene alcohol selective oxidation. This work, on the one hand, opens up an efficient way to generate 1O2 by O2 activation in peroxide-based catalytic oxidations, and on the other hand, develops a bifunctional Fe1–N4 single-atom site with rapid electron gain and loss ability, which sheds light on further improving catalytic performance in single-atom catalysts via relay catalysis mechanism.